It may seem obvious, but the best advice I can give is enjoy yourself. If you aren't having fun in and around your gold making, you won't keep it up. Of course that doesn't mean that every second has to be fun: nobody ever enjoyed milling herbs to make inks to make glyphs. But if you can be doing these things in an enjoyable setting, it will make it easier. For instance, your milling might take place in the few minutes between queueing for an instance and getting in; or while waiting for your raid group to assemble; a time when you've nothing better to do,anyway, and you get to feel you aren't wasting your time during these waits. Or you might be gathering your herbs or ores or leather or fish or meats while running daily quests you'd already be doing (rather than setting out specifically to gather stuff).

Or you might have a pleasurable goal in mind that lessens the pain of the dull bits of gold-making. Enjoying yourself might be as simple as being able to point to the progress you made towards some goal, whether it's a long-term one like "hit the gold cap" or a short-term one like "make enough flasks so that I've plenty to post on raid day".

Some people camp the Auction House. You might enjoy that for a few weeks or even a few month, but believe me, in the long-term, you need to be adventuring in Azeroth, or you'll tire of it. Get out and have fun.